The present invention relates generally to the bonding together of two similarly shaped portions of thermoplastic articles and more particularly involves friction welding of upper and lower container sections made of dissimilar plastics, to provide a single hermetically welded container.
The prior art discloses a method of welding container sections together to form a single container, which method is directed to cylindrically shaped thermoplastic containers which are rotated at high speeds against each other to generate by friction the heat necessary to bond the two sections together. This prior art method is commonly referred to as spinwelding and is disclosed in such patent patents as U.S. Pat. No. 3,297,504, U.S. Pat. No. Re. 29,448 and U.S. Pat. No. 3,499,068.
While the prior art method of spinwelding is advantageous over such methods as chemical bonding, cementing and thermal bonding by means such as laser, electon beam, radio wave, and electrical means, it offers disadvantage in that it is restricted to cylindrical joints. Obviously two non-cylindrical container sections could not be successfully spinwelded because of their lack of surfaces which would maintain contact during relative rotary motion between them.
The present invention overcomes the disadvantage of rotary spinwelding by providing methods and apparatus for friction welding thermoplastic containers having non-cylindrical joinder sections as well as being applicable also to cylindrical sections. The present invention utilizes an external heat source combined with oscillatory motion, rather than rotary motion, between the two sections to be joined to provide the friction for generating the final stage of heating for bonding the two sections. Dissimilar plastics can be bonded using the present methods and apparatus.